The present invention relates to an image forming method and an image forming apparatus, both to form images electrophotographically on recording paper by controlling image forming conditions, and more particularly to image density control technology.
For a conventional image forming apparatus, such as copying machine or printer, that has a developing device constructed so that a latent image formed on its photoreceptor is developed using a two-component developing agent consisting of toner and carrier, an image density control method is employed in which the toner concentration in the developing agent is maintained by replenishing toner according to the amount of toner which has been consumed during the development.
The above-mentioned toner addition is controlled so as to be performed when a decrease in toner concentration is detected by, for example, detecting the resistance or permeability of the developing agent.
With this conventional method, however, there is a limit to supplying high-quality images stably over long periods of time, because detection errors are prone and partly because changes in the developing performance of the developing agent cannot be properly accommodated.
There is a method of controlling image forming conditions to avoid such inconveniences in image density control as described above. That is to say, this method forms a control patch on the photoreceptor, then detects the image density of the control patch by use of a density detection means, and controls image forming conditions using the detection signal sent from the density detection means.
Image density control using this method has the characteristic that since the image density of the image actually formed is constantly maintained, almost no control errors basically occur.
With regard to such image density control, the applicant for the present patent performed several proposals in Unexamined Japanese Application Patent Laid-Open Publications Nos. Hei 07-137346 and 2000-181155.
Under this image density control method, a control patch is formed on an image forming body such as a photoreceptor in accordance with image data of a reference density, then the image density of the formed control patch is detected using an image density detection means, and the quantity of electric charge, the exposure amount, the developing bias, the developing agent carrying velocity, the concentration of the toner in the developing agent, and other image forming conditions are controlled using the detection signal sent from the image density detection means.
Under prior art, a control patch is formed on an image forming body such as a photoreceptor in accordance with the image data relating to reference density, then the image density of the formed control patch is detected using an image density detection means, and the quantity of electric charge, the exposure amount, the developing bias, the developing agent carrying velocity, the toner concentration in the developing agent, and other image forming conditions are controlled using the detection signal sent from the image density detection means.
In this case, a patch that has been formed as an image of the required density by varying the developing bias and the charging potential is usually used as a reference control patch. However, since it is difficult with the above-mentioned control method to respond to the tendencies towards faster image formation and toner particle size reduction in recent years, the formation of a dither pattern and an error diffusion pattern for imagewise exposure based on reference input density image data, or of solid and non-solid reference patterns with densities adjusted by laser pulse width modulation has been proposed. Hereby, although, heretofore, the developing field has been reduced by reducing the developing bias voltage in order to obtain a patch image with almost the maximum density, a patch image that stably changes in density can be obtained using the method proposed above.
Even when a control patch is formed by imagewise exposure based on image data of a reference input density, since changes in the sensitivity of the photoreceptor, associated with changes in the temperature and humidity of the ambient environment, and the deterioration in the characteristics of the developing agent change the quality of the control patch formed, a control patch more stable in image density must be formed to provide optimal control of the image forming conditions.
In the meantime, although, as described above, the image density control method using a control patch is useful technology, it has become clear that this method poses problems associated particularly with the image formation in which the image forming rate is increased or toner is reduced in particle size, such as polymerized toner, is used.
For example, during a continuous image forming process, although a control patch is formed in both the leading image area and the following image area, it is difficult to make setting of the image forming conditions for the control patch follow the progress of the image forming process.
More specifically, although the conventional formation of a control patch has been reducing the developing bias voltage value and charging potential value during the normal image forming process, there have occurred the problems that the slow response speeds of the charging device and developing bias power supply have resulted in the control patch becoming unstable in density or the end portion of the normal image area being becoming uneven in density.
Also, although the conventional control patch is formed as an image of uniform density (generally called xe2x80x9csolid imagexe2x80x9d), since the solid image is not stable against changes in image forming conditions and suffers changes in the density of the control patch due to time-varying changes in the developing performance of the developing agent, the conventional control method has the problem that although it basically is useful density control technology, it reduces the control accuracy of the image forming conditions for normal image formation.
Accordingly, there arises the problem that when the density detection means detects a decrease in the density of the control patch below the required value due to an extended time of use of the developing agent, since an excessive amount of toner will be added, image density will increase too significantly and the toner will scatter.
Such a discrepancy between the density of the control patch and that of the image actually formed is particularly significant in the case of using polymerized toner.
In order to solve the above new problems, the present inventors have improved the control of image forming conditions, based on the formation of a control patch of stable density, by dither-patterning the above-mentioned control patch.
However, even under the configuration that uses a control patch of stable density, since changes in the sensitivity of the image forming body according to ambient temperature and humidity or changes in the characteristics of the developing agent also change, although slightly, the density of the control patch, it has been found that density control technology still admits of improvement.
The first object of the present invention is to supply an image forming method, and an image forming apparatus, by which the optimal density of a control patch not affected by changes in the sensitivity of the image forming body or changes in the response characteristics of writing light according to the particular type of exposure means can be obtained and thus the formation of images with stable image density can be maintained over long periods of time.
The second object of the present invention is to supply an image forming method, and an image forming apparatus, by which a control patch of image density can be stably formed to control image forming conditions either during the warming-up time following the power-on sequence of the image forming apparatus or after the required number of images have been printed.
The third object of the present invention is to supply an image forming apparatus constructed so that a control patch of image density is stably formed after replacement, adjustment, or other maintenance operations of an exposure device used to form a latent image using the image forming apparatus.
The above objects can be achieved by adopting either one of the following structures (1) to (57):
(1) An image forming method by which the formation of an image is accomplished by detecting the density of a control patch which has been formed by exposure based on image data of reference input density, and controlling image forming conditions in accordance with the corresponding detection signal, wherein the image forming method is characterized in that the control patch consists of a dither pattern.
(2) The image forming method in Structure (1) above, characterized in that the reference input density for forming the dither pattern is changed according to the particular environmental parameters.
(3) The image forming method in Structure (1) or (2) above, characterized in that the reference input density for forming the dither pattern is changed according to the quantity of image formation.
(4) The image forming method in either of Structures (1) to (3) above, characterized in that the reference input density for forming the dither pattern is changed according to the particular stirring period of time of the developing agent.
(5) The image forming method in either of Structures (1) to (4) above, characterized in that the developing agent carrying velocity of the developing agent carrying body is made variable, and in that after the reference value of the developing agent carrying velocity has been set, when the developing agent carrying velocity is less than the reference value, image density adjustment is accomplished by changing the developing agent carrying velocity, and when the developing agent carrying velocity reaches the reference value, image density adjustment is accomplished by replenishing the developing device with toner.
(6) The image forming method in either of Structures (1) to (5) above, characterized in that polymerized toner is used for development.
(7) An image forming apparatus comprising an image forming body, a latent image forming means that forms an electrostatic latent image on the image forming body in accordance with image data, a developing means having a developing agent carrying body that forms a toner image by developing the electrostatic latent image formed on the image forming body, a toner replenishment means for replenishing toner to the developing means, an image density detection means for detecting the image density of the toner image formed on the image forming body, and a control means, wherein the image forming apparatus is characterized in that the control means forms a control patch on the image forming body by controlling the latent image forming means and thus controls image forming conditions in accordance with the output of the image density detection means which has detected the image density of the control patch, and in that a patch consisting of a non-solid pattern is used as the control patch.
(8) The image forming apparatus in Structure (7) above, characterized in that when the developing agent carrying velocity is less than its reference value, the control means executes the first image density control to adjust the developing agent carrying velocity of the developing agent carrying body, and when the developing agent carrying velocity reaches the reference value, the control means executes the second image density control for toner replenishment of the toner replenishment means without adjusting the developing agent carrying velocity.
(9) The image forming apparatus in Structure (7) or (8) above, characterized in that the density value of the image data for forming the non-solid pattern is changed according to the particular environmental parameters.
(10) The image forming apparatus in either of Structures (7) to (9) above, characterized in that the density value of the image data for forming the non-solid pattern is changed according to the particular quantity of image formation.
(11) The image forming apparatus in either of Structures (7) to (10) above, characterized in that the density value of the image data for forming the non-solid pattern is changed according to the particular stirring time of the developing agent.
(12) An image forming method by which image density control A executed before or after an image forming process, and image density control B executed during the image forming process are conducted in accordance with the detection results relating to the image density of a control patch which has been formed on an image forming body, wherein the image forming method is characterized in that a non-solid pattern is used as the control patch.
(13) The image forming method in Structure (12) above, characterized in that the image density control A is conducted when power is supplied to the image forming apparatus.
(14) The image forming method in Structure (12) or (13) above, characterized in that the image density control A is conducted at fixed time intervals under a stand-by status.
(15) The image forming method in either of Structures (12) to (14) above, characterized in that the image density control A is conducted at each required time.
(16) The image forming method in either of Structures (12) to (15) above, characterized in that image density detection of the control patch under the image density control A, and image density control of the control patch under the image density control B are conducted by one image density detection means.
(17) The image forming method in either of Structures (12) to (16) above, characterized in that during the image density control B, toner is replenished each time the predetermined number of images is formed.
(18) The image forming method in either of Structures (12) to (17) above, characterized in that polymerized toner is used for development.
(19) An image forming apparatus comprising an image forming body, a latent image forming means that forms an electrostatic latent image on the image forming body in accordance with image data, a developing means having a developing agent carrying body and to form a toner image by developing the electrostatic latent image formed on the image forming body, a toner replenishment means for replenishing the developing means with toner, an image density detection means for detecting the image density of the toner image formed on the image forming body, and a control means, wherein the image forming apparatus is characterized in that when image density control A executed before or after an image forming process, and image density control B executed during the image forming process are conducted, the control means forms the control patch consisting of a non-solid pattern.
(20) The image forming apparatus in Structure (19) above, characterized in that when power is supplied to the image forming apparatus, the control means executes the image density control A.
(21) The image forming apparatus in Structure (19) or (20) above, characterized in that the control means executes the image density control A at fixed time intervals under a stand-by status.
(22) The image forming apparatus in either of Structures (19) to (21) above, characterized in that the control means executes the image density control A at each required time.
(23) The image forming apparatus in either of Structures (19) to (22) above, characterized in that during the image density control B, the control means functions to replenish toner each time a predetermined number of images is formed.
(24) An image forming method by which the formation of an image is accomplished by detecting the density of a control patch formed by exposure based on image data of reference input density, and controlling the image forming conditions in accordance with the corresponding detection signal, wherein the image forming method is characterized in that the control patch composed of a non-solid pattern is used and, in that latent images are formed by converting image data having reference input densities different from each other, then the potentials of the plurality of patches on which the electrostatic latent images have been formed are detected, and the single density value of the image data corresponding to the desired patch potential is calculated from all detected patch potentials.
(25) The image forming method in Structure (24) above, characterized in that the reference input density to be used to form the non-solid pattern is changed according to the particular environmental parameters.
(26) The image forming method in either of Structure (24) or (25) above, characterized in that the density value of the image data for forming the non-solid pattern is changed according to the particular quantity of image formation.
(27) The image forming method in either of Structures (24) to (26) above, characterized in that the density value of the image data for forming the non-solid pattern is changed according to the particular stirring period of time of the developing agent.
(28) The image forming method in either of Structures (24) to (27) above, characterized in that the calculation of the density value of the image data corresponding to the desired patch is performed each time a predetermined number of images is formed.
(29) The image forming method in either of Structures (24) to (28) above, characterized in that the calculation of the density value of the image data corresponding to the desired patch is performed for each predetermined period of developing agent stirring time.
(30) An image forming method comprising the process of conducting imagewise exposure of a solid patch on the image forming body which has been electrically charged to a potential VH by a charging device and performing potential adjustments between the latent image potential VL of the solid patch and a developing bias VB, the process of forming a plurality of non-solid control patches on the image forming body by modifying image data, and the process of detecting the potential of each non-solid patch by use of a potential sensor and performing arithmetic operations to obtain the desired patch potential, and characterized in that an image can be formed by detecting the derived density of the non-solid patch and controlling image forming conditions using the resulting detection signal.
(31) An image forming apparatus comprising an image forming body, an electrical charging means for charging the image forming body, an imagewise exposure means for conducting imagewise exposure based on image data and enabling the adjustment of the amount of light necessary to form an electrostatic latent image on the image forming body, a potential measuring means for measuring the potential of the image forming body, a developing means having a developing agent carrying body and to form a toner image by applying a developing bias and reversal-developing the electrostatic latent image on the image forming body, an image density detection means for detecting the image density of the toner image formed on the image forming body, and a control means, and characterized in that the control means forms an image using either one of the image forming method set forth in Structure (30).
(32) An image forming apparatus comprising an image forming body, an electrical charging means for charging the image forming body, an imagewise exposure means for conducting imagewise exposure based on image data and enabling the adjustment of the amount of light necessary to form an electrostatic latent image on the image forming body, a potential measuring means for measuring the potential of the image forming body, a developing means having a developing agent carrying body for forming a toner image by applying a developing bias and reversal-developing the electrostatic latent image on the image forming body, an image density detection means for detecting the image density of the toner image formed on the image forming body, and a control means, and characterized in that immediately after changing the intensity of the imagewise exposure means, the control means forms an image using either of the image forming method set forth in Structure (30).
(33) An image forming method comprising the process of forming latent images of a plurality of control patches on an image forming body by use of writing light based on a plurality of sets of image data mutually different in reference input density, the process of measuring the latent image potentials of the control patches by use of a potential detection means, and the process of performing arithmetic operations on the relationship between each latent image potential mentioned above and each reference input density mentioned above and then deriving the density (P1) of the control patch that becomes the required latent image potential, while at the same time storing the results into a storage means, and to form an image by controlling image forming conditions in accordance with the density detection signal generated after development of the control patch having the density (P1), wherein the image forming method is characterized in that the temperature (T1) of the image forming body during arithmetic operations is detected by a temperature detection means and stored into a storage means and in that when the temperature of the image forming body during the formation of the control patch having the density (P1) is changing with respect to the temperature (T1), the density (P1) of the corresponding control patch is changed according to the particular amount of change in the temperature of the image forming body.
(34) The image forming method in Structure (33) above, characterized in that the control patch consists of a dither pattern.
(35) The image forming method in Structure (33), characterized in that the control patch consists of an error diffusion pattern.
(36) The image forming method in Structure (33), characterized in that the control patch consists of a laser pulse width modulation pattern.
(37) The image forming method in Structure (33), characterized in that the density of the control patch that is changed according to the particular change in temperature is further changed according to the particular changes in environmental conditions.
(38) An image forming method comprising the process of forming latent images of a plurality of control patches on an image forming body by use of writing light based on a plurality of sets of image data mutually different in reference input density, the process of measuring the latent image potentials of the control patches by use of a potential detection means, and the process of performing arithmetic operations on the relationship between each latent image potential mentioned above and each reference input density mentioned above and then deriving the density (P1) of the control patch that becomes the required latent image potential, while at the same time storing the results into a storage means, and to form an image by controlling image forming conditions in accordance with the density detection signal generated after development of the control patch having the density (P1), wherein the image forming method is characterized in that the threshold data to be used for the arithmetic operations is changed according to the sensitivity of the image forming body that has been stored into a storage means beforehand.
(39) The image forming method in Structure (38), wherein the control patch is characterized in that it consists of a dither pattern.
(40) The image forming method in Structure (38), wherein the control patch is characterized in that it consists of an error diffusion pattern.
(41) The image forming method in Structure (38), wherein the control patch is characterized in that it consists of a laser pulse width modulation pattern.
(42) The image forming method in Structure (38), characterized in that the threshold data to be used to derive the density of the control patch is changed according to the particular changes in environmental conditions.
(43) The image forming method in Structure (38), characterized in that the threshold data to be used to derive the density of the control patch is changed according to the number of sheets to be printed.
(44) The image forming method in Structure (38), characterized in that the threshold data to be used to derive the density of the control patch is changed according to the particular stirring period of time of the developing agent.
(45) An image forming method comprising the process of forming latent images of a plurality of control patches on an image forming body by use of writing light based on a plurality of sets of image data mutually different in reference input density, the process of measuring the latent image potentials of the control patches by use of a potential detection means, and the process of performing arithmetic operations on the relationship between each latent image potential mentioned above and each reference input density mentioned above and then deriving the density (P1) of the control patch that becomes the required latent image potential, while at the same time storing the results into a storage means, and to form an image by controlling image forming conditions in accordance with the density detection signal generated after development of the control patch having the density (P1), wherein the image forming method is characterized in that the threshold data to be used for the arithmetic operations is changed according to the response characteristics of the writing light that have been stored into a storage means beforehand.
(46) The image forming method in Structure (45), characterized in that the control patch consists of a dither pattern.
(47) The image forming method in Structure (45), characterized in that the control patch consists of an error diffusion pattern.
(48) The image forming method in Structure (45), characterized in that the control patch consists of a laser pulse width modulation pattern.
(49) The image forming method in Structure (45), characterized in that the threshold data to be used to derive the density of the control patch is changed according to the particular changes in environmental conditions.
(50) The image forming method in Structure (45), characterized in that the threshold data to be used to derive the density of the control patch is changed according to the number of sheets to be printed.
(51) The image forming method in Structure (45), characterized in that the threshold data to be used to derive the density of the control patch is changed according to the particular stirring period of time of the developing agent.
(52) The image forming method in either Structure (33), (38), or (45), characterized in that polymerized toner is used for development.
(53) An image forming apparatus comprising a latent image forming means that forms latent images of a plurality of control patches on the image forming body in accordance with a plurality of sets of image data mutually different in reference input density, a potential detection means for detecting the latent image potentials of the control patches, an arithmetic operating means for performing arithmetic operations on the relationship between each latent image potential mentioned above and each reference input density mentioned above and then deriving the density (P1) of the control patch that becomes the required latent image potential, a storage means into which the control patch having the derived density (P1) is stored, a temperature detection means for detecting the temperature (T1) of the image forming body during arithmetic operations, a storage means into which the temperature that has been detected by the temperature detection means is stored, a developing means having a developing agent carrying body and to form a toner image by developing a latent image of the control patch formed on the image forming body, and a density detection means for detecting the density of the toner image of the control patch that has been developed, and a control means, wherein the image forming apparatus is characterized in that it can control image forming conditions by first judging whether the temperature (T1) of the image forming body during the formation of the control patch in copy sequence mode is changing with respect to the temperature (T1) of the image forming body during arithmetic operations on the density of the control patch, next changing the density (P1) of the control patch according to the particular difference between the above temperatures, then developing the latent image that has been exposed to light so as to achieve the optimal patch density, and finally, receiving the density signal corresponding to the control patch toner image density detected by the density detection means.
(54) The image forming apparatus in Structure (53) above, characterized in that the control patch consists of either one of a dither pattern, an error diffusion pattern, and a laser pulse width modulation pattern.
(55) The image forming apparatus in Structure (53), characterized in that a storage means that contains the sensitivity of the image forming body beforehand is provided, in that the threshold data to be used for the arithmetic operations performed to derive the density of the control patch is changed according to the sensitivity of the image forming body that has been stored into the storage means, and in that the corresponding arithmetic operations are performed by the arithmetic operating means.
(56) The image forming apparatus in Structure (53), characterized in that a storage means that contains beforehand the response characteristics of the writing light of the writing means which constitutes the latent image forming means is provided, in that the threshold data to be used for the arithmetic operations performed to derive the density of the control patch is changed according to the response characteristics of the writing light that have been stored into the storage means, and in that the corresponding arithmetic operations are performed by the arithmetic operating means.
(57) The image forming apparatus in Structure (53), characterized in that polymerized toner is used for the development.